Add a "fork" of musl as //fusl.

fusl/src/multibyte/internal.h

+/* 
+ * This code was written by Rich Felker in 2010; no copyright is claimed.
+ * This code is in the public domain. Attribution is appreciated but
+ * unnecessary.
+ */
+
+#define bittab __fsmu8
+
+#include <stdint.h>
+
+#ifdef __PIC__
+__attribute__((__visibility__("hidden")))
+#endif
+extern const uint32_t bittab[];
+
+/* Upper 6 state bits are a negative integer offset to bound-check next byte */
+/*    equivalent to: ( (b-0x80) | (b+offset) ) & ~0x3f      */
+#define OOB(c,b) (((((b)>>3)-0x10)|(((b)>>3)+((int32_t)(c)>>26))) & ~7)
+
+/* Interval [a,b). Either a must be 80 or b must be c0, lower 3 bits clear. */
+#define R(a,b) ((uint32_t)((a==0x80 ? 0x40u-b : 0u-a) << 23))
+#define FAILSTATE R(0x80,0x80)
+
+#define SA 0xc2u
+#define SB 0xf4u
+
+/* Arbitrary encoding for representing code units instead of characters. */
+#define CODEUNIT(c) (0xdfff & (signed char)(c))
+#define IS_CODEUNIT(c) ((unsigned)(c)-0xdf80 < 0x80)
+
+/* Get inline definition of MB_CUR_MAX. */
+#include "locale_impl.h"